This invention relates to a new process for the production of aminobenzylamines and particularly, to a process useful for industrial practice.
The aminobenzylamines are an important substance as a curing agent for epoxy resins, a starting material for polyamides and polyimides and a material for intermediates of agricultural chemicals.
It is, hitherto, known that aminobenzylamines are produced starting from nitrobenzaldehyde or nitrobenzonitrile.
As for the former, there are known the following processes:
(1) Nitrobenzylbromide is derived from nitrobenzaldehyde, which is then reacted with potassium phthalimide to obtain N-(m-nitrobenzyl)-phthalimide, and m-aminobenzylamine is produced with an yield of about 20% by a two-step reduction reaction (N. Kornblum et al, J. Am. Chem. Soc., 71, 2137 (1949)).
(2) m-Nitrobenzaldehyde is reacted with phenylhydrazine and the resulting hydrazone compound is catalytically reduced whereby m-aminobenzylamine is obtained with an yield of 60% (A. Siddiqui et al, Synth. Commn. 7, 71-78 (1977)).
(3) Starting from m-nitrobenzaldehyde, m-nitrobenzaldoxime is formed, which is then catalytically reduced under a high pressure by means of Raney nickel catalyst whereby m-aminobenzylamine is obtained with an yield of 52% (J. R. Griffith et al, NRL Report 6439).
On the other hand, processes starting from the latter are as follows:
(4) p-Aminobenzonitrile derived from p-nitrobenzonitrile is reduced by lithium aluminum hydride and thus, p-aminobenzylamine is obtained with an yield of 37% (N. C. Brown et al, J. Wedicinal Chem., 20 1189 (1977)).
(5) By catalytically reducing m-nitrobenzonitrile with Raney nickel under a high pressure, m-aminobenzylamine is obtained with an yield of 49% (J. R. Griffith et al, NRL Report 6439).
As mentioned above, according to processes (1) and (2), a relatively expensive compound such as potassium phthalimide and phenylhydrazine is used in the amount of more than equivalent and the resulting intermediate is reduced to obtain end products. However, these processes have disadvantages that the reaction steps are complicated and for recovery of the by-products expenses and labour are required. Process (4) has disadvantages that the reducing agent is expensive and difficult in handling. As for processes (3) and (5) of using Raney nickel catalyst and effecting the catalytic reduction in an autoclave under a high pressure, there are disadvantages that the apparatus are expensive and the volume efficiency is low.
Generally, in a process for producing benzylamines by a conventional reduction method from benzonitriles or benzaldoximes, the yield of benzylamine is low because of by-producing secondary amines and ammonia. For example, in case of catalytically reducing benzonitrile in ethanol with a Ni catalyst, the yield of benzylamine is 40-50% and the yield of dibenzylamine is 20% (Ed. by Nippon Kagakukai, "Jikken Kagaku Koza" Vol. 17, Maruzen, 313 (1956)). Also, in case of catalytically reducing benzaldoxime in water/alcohol with a Pd colloidal catalyst, the yield of benzylamine is 47% and the yield of dibenzylamine is 41% (W1, Gulewitsch. Ber., 57 1645 (1924)).
This reason is explained as follows: in both the reductions of benzonitrile and benzaldoxime, benzalimine is formed at the beginning, which causes various reactions such as formation of benzaldehyde due to hydrolysis of benzalimine and condensation of benzalimine with benzaldehyde. Thus, the resulting by-products bring about low yield of benzylamine.
Accordingly, for the purpose of controlling the formation of such by-products and improving the yield of benzylamine, there are provided processes using acetic anhydride or dried hydrogen chloride in the reduction step. For example, in case of effecting the reduction with use of acetic anhydride in the amount of 2.65 mols per mol of benzonitrile, benzylamine is obtained with an yield of 69% and in case of 12.7 mols the yield is 91% (W. H. Carothers et al, J. Am. Chem. Soc., 47 3051-3057 (1925); F. E. Gould et al J. Org. Chem., 25 1658-1660 (1960)).
Also, by reaction of benzaldoxime with acetic anhydride benzaldoxime acetate is formed, which is then reduced, thus benzylamine being obtained with 91% (K. W. Rosenmund et al, Ber., 56 2258-2262 (1923)). These processes of reducing benzonitrile or benzaldoxime in the acetic anhydride solvent comprise isolating N-acetylbenzylamine and hydrolysing same to obtain benzylamine.
On the other hand, according to a process using dried hydrogen chloride, the dried hydrogen chloride gas is used in the amount of more than 1 equivalent for benzonitrile and of more than 3 equivalents for benzaldoxime and thus benzylamine is obtained with high yield (W. H. Hartung, J. Aw. Chem. Soc., 50 3370-3374 (1928)).
As mentioned above, the reduction process of benzonitrile or benzaldoxime using acetic anhydride or dried hydrogen chloride is effective for improving the yield of benzylamine, in which the acetic anhydride and hydrogen chloride are considered as having a function of stabilizing the intermediate in the course of the reduction and as exhibiting an effect of catching water formed in case of benzaldoxime thereby controlling the decomposition reaction. However, the process using acetic anhydride has the disadvantage that a comparatively expensive acetic anhydride must be used in a large quantity. Also, as for the process using dried hydrogen chloride, it is necessary to use the solvent in anhydrous condition and also, due to the delay of hydrogen absorption a diluted solution is required and there is a serious disadvantage that the deterioration of catalyst is remarkable and the material of apparatus is injured.
In case the above processes are applied for the reduction of nitrobenzaldoxime in addition to the above problems further complicated reactions are expected due to the nitro group. Namely, there are considered a reaction with an amino group formed by reduction of the nitro group, a hydrolysis caused by water formed and a side reaction of aminobenzaldehyde formed by this hydrolysis. For controlling these side reactions, it is necessary to use the acetic anhydride or dried hydrogen chloride in further large quantities.
Therefore, it is to be noticed that it is very difficult to produce aminobenzylamine in a commercial scale by the conventional processes.